CO₂e, or carbon dioxide equivalent, is the unit that expresses different greenhouse gases as a single comparable number. Each gas is multiplied by its global warming potential (GWP), the measure of how much heat it traps relative to carbon dioxide over a set period, conventionally 100 years. The results add up into one total.
Why It Matters for Manufacturers
Industrial operations emit far more than carbon dioxide. Methane leaks from natural gas systems, nitrous oxide is released during combustion and certain chemical processes, hydrofluorocarbons escape from chillers and refrigeration, and sulfur hexafluoride sits inside electrical switchgear. The GHG Protocol requires the seven gases it identifies as required by the UNFCCC/Kyoto Protocol — carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, sulfur hexafluoride and nitrogen trifluoride — and a manufacturer that counts only fuel-related CO₂ is underreporting.
The conversion factors are not fixed. GWP values are revised with each IPCC assessment cycle, so a company that moves from AR5 to AR6 values will see its total change without a single operational thing happening. That has to be explained in the disclosure and handled consistently in any restated baseline.
This is also an audit question rather than a technical footnote. Assurance providers check which GWP source and vintage were used and whether the same set was applied across every site and every gas. Where an inventory is assembled from plant-level spreadsheets, mixed vintages are a common and avoidable finding.
U.S. and EU Applicability
ESRS E1 requires companies to use the most recent 100-year GWP values published by the IPCC. Where emission factors based on older GWP values are the most suitable or available, a company may use them but must disclose which GWPs its inventory is based on. IFRS S2 also points to the most recent IPCC values, though December 2025 amendments allow companies to use other GWP values, in whole or in part, where a jurisdiction or an exchange requires them.
In the U.S., CARB proposed at its July 21, 2026 workshop that reporting entities disclose the GWP values and assessment report vintage they used. That is a pre-proposal staff concept for the 2027 SB 253 framework rather than an adopted requirement, and CARB has not specified a required vintage.
Current Status
Last updated: Aug. 31, 2026
- The AR6 GWP-100 values in the GHG Protocol‘s published table, which is what corporate reporters are directed to use, include carbon dioxide at 1, fossil methane at 29.8, non-fossil methane at 27.0 and nitrous oxide at 273. Two changes from AR5 matter for restatements: AR6 includes the carbon-cycle response for non-CO₂ gases in its headline values, where AR5’s headline values did not, and AR6 sets separate values for fossil and biogenic methane. National inventories under the UNFCCC still use AR5 values.
- The ISSB’s amendments to IFRS S2, which include the GWP relief above, are effective for reporting periods beginning on or after Jan. 1, 2027, with early application permitted.
- The revised ESRS were adopted July 3, 2026 and apply to financial years beginning on or after Jan. 1, 2027. For financial year 2026 a company may apply the revised standards early or the existing standards with specified reliefs, stating in its sustainability statement which version it used. As of Aug. 31, 2026 the acts are not yet published in the Official Journal, and early adoption becomes available once they enter into force.
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